Traditional methods for producing battery plates for lead-acid batteries generally involve a mixing, curing and drying operation in which the active materials in the battery paste undergo chemical and physical changes that are used to establish the chemical and physical structure and subsequent mechanical strength necessary to form the battery plate. To produce typical battery plates, materials are added to commercial paste mixing machines common in the industry in the order of lead oxide, flock, water and sulfuric acid, which are then mixed to a paste consistency. Conventional additives such as a flock or expander may also be used to modify the properties of the paste and the performance of the plates produced therefore. During mixing, chemical reactions take place in the paste producing basic lead sulfates, the most common of which is tribasic lead sulfate. The final paste composition is a mixture of basic lead sulfates, unreacted lead monoxide and residual free lead particles.
Pasting is the process of making a battery plate from the paste mix. This paste is dispensed into a commercial automatic pasting machine of a type common in the industry which applies the paste to a grid structure composed of a lead alloy. The paste is dispensed into a hopper on the pasting machine and from there the paste is applied to the grids at high speed. The pasted plates are generally surface dried in a tunnel dryer of a type common in the industry and then either stacked in columns or placed on racks. The stacked or racked plates are then placed in heated curing chambers. In these chambers the plates are subjected to temperatures of 70° C.-80° C. in a high humidity atmosphere for up to several days to convert the tribasic lead sulfate in the plates to tetra basic lead sulfate and to allow oxidation of the residual free lead. The plates are then dried, and the finished plates are then ready for assembly into batteries.
Two key factors important in the curing process are the formation of a proper crystal structure by converting tribasic lead sulfate (TRBLS) formed during paste mixing into tetra basic lead sulfate (TTBLS), and the formation of tetragonal lead oxide by oxidizing residual free lead metal. Generally, a crystal structure high in tetra basic lead sulfate will increase battery life. The general formula for converting tribasic lead sulfate to tetra basic lead sulfate is set forth below:3PbO.PbSO4.H2O+PbO--->4PbO.PbSO4+H2O
A common problem with traditional battery paste compositions and methods for curing is that the chemical characteristics of the resultant plates are not uniform, varying in quality. Other common problems include difficulty in the repeatability of production, uncertain and/or lengthy curing time, the large number of curing chambers needed to process plates, and high capital and energy costs. Overall, the curing process is labor, capital and energy intensive and the composition of the plates is frequently variable which leads to variability in the batteries that are made from them.
Consequently, a need exists for improvements in battery pastes which may be used with conventional paste mixing processes, procedures and equipment to produce positive and/or negative battery plates having greater uniformity, more consistent quality, more consistent reproducibility, all while eliminating the curing process, procedure and equipment so as to reduce the cost and speed up the production of batteries.
Various processes and procedures for battery pastes and the production of battery plates are known. The following is a discussion of such known processes and procedures.
U.S. Pat. No. 5,302,476 entitled “High Performance Positive Electrode for a Lead-acid Battery,” issued to Kao et al. on Apr. 12, 1994, discloses battery paste compositions and methods of using the paste to make electrodes suitable for use as a lead-acid battery plate. The paste consists essentially of a basic lead sulfate component, preferably a mixture of about 0-100% TRBLS and about 0-75% TTBLS, a persulfate salt such as sodium persulfate, potassium persulfate, calcium persulfate or ammonium persulfate, lead oxide and preferably 10-30% water. The paste is applied to the surface of an electrode, which is then air dried prior to formation. The electrode is formed in excess sulfuric acid by passing a constant current through the electrode for a sufficient period of time.
Kao et al.'s paste differs from the battery paste of the present disclosure, for example, by utilizing a persufate as an oxidizing agent, which the battery paste of the present disclosure does not use. Another difference, for example, is in the use of conductive metal oxides in Kao et al.'s paste, which the battery paste of the present disclosure does not use. Further, Kao et al.'s paste does not disclose a micronized tetra basic lead sulfate nor a low-free-lead oxide as in the battery paste of the present disclosure. The battery paste of the present disclosure does not require the addition of an oxidizing agent or a conductive additive. Additionally, the methods for producing the respective battery plates differ significantly.
U.S. Pat. No. 6,755,874 and U.S. Patent Application No. 2002/0124388, both entitled “Plate Making Process for Lead Acid Battery, issued and published to Chen et al. on Jun. 29, 2004 and Sep. 12, 2002 respectively, disclose plate making processes for lead-acid batteries wherein the steps of mixing, reacting and crystallizing occur in a closed reactor under controlled temperature and mixing conditions to produce a paste having the desired crystal morphology. A polymer is then added to the paste to bind the crystals together and to produce desired rheological properties in the paste.
Unlike the paste of the present disclosure, Chen et al.'s paste is made in situ by heating leady oxide and sulfuric acid in a mixer until tetra basic lead sulfate is formed. The resulting paste is combined with a polymer to give strength to the battery plates. This differs substantially from the paste of the present disclosure which is made from a low (or no) free lead oxide and micronized tetra basic lead sulfate.
U.S. Pat. No. 4,713,304, entitled “Method of Preparing Lead-Acid Battery Plates and Lead-Acid Batteries Containing Plates So Prepared,” issued to Rao et al. on Dec. 15, 1987, discloses a method for preparing lead-acid battery positive and negative battery plates. The method comprises the steps of applying wet leady oxide paste to battery grids to form plates, optionally wrapping the freshly pasted plates with an absorbent material, and initiating formation of the plates while the plates contain more than about 5 wt. % free lead in the paste and are generally damp from moisture existing in the paste from the time of plate pasting.
Rao et al.'s paste differs considerably from the paste of the present disclosure, for example, by making a paste from conventional materials and then wrapping the wet, uncured plates in an absorbent material and assembling the battery from the resulting wrapped plates. The plates are then charged in the battery container. It should be readily apparent that the method of producing the respective battery plates differs significantly.
U.S. Pat. No. 5,314,766 entitled “Lead-Acid Battery Electrode and Method of Manufacture” and U.S. Pat. No. 5,252,105 entitled “Method of Forming Lead-Acid Battery Electrode,” issued to Witherspoon et al. on May 24, 1994 and Oct. 12, 1993 respectively, each disclose paste compositions and methods of forming lead-acid battery electrodes for lead-acid batteries.
With respect to the '776 patent, a “pre-charged” positive electrode is made from partially oxidized tetra basic lead sulfate mixed with lead dioxide and binders. The wet mixture is applied to the oxidized surface of a lead support substrate, and then heated and pressed for a time and at a temperature and compressive load sufficient to form an adhered or retained coating of active material on the substrate. It should be readily apparent that the method of producing the respective battery plates differs significantly.
With respect to the '105 patent, a battery paste is made from a mixture of monobasic lead sulfate and red lead which is pasted onto a grid and then heated for up to 30 minutes. Tetra basic lead sulfate is formed during the heating step. Again, it should be readily apparent that the method of producing the respective battery plates differs significantly.
U.S. Pat. No. 5,290,359 entitled “Apparatus for Production of a Battery Paste,” issued to Coonen et al. on Mar. 1, 1994, and U.S. Pat. No. 5,096,611 entitled “Process for the Production of Battery Paste,” issued to Matthew et al. (sic) on Mar. 17, 1992, disclose a process for making battery paste which includes producing a slurry containing tri- and tetra-based lead sulfates, formed in a continuously stirred tank reactor. The process of these patents involves a complex series of mechanical and process steps to make battery paste in a continuous manner. It also uses an oxidizing agent in the paste. The methods for producing these battery plates and the battery plate of the present disclosure differ significantly.
The present disclosure overcomes the disadvantages and/or shortcomings of known prior art battery pastes and methods for producing battery plates, and provides a significant improvement thereover. The present disclosure provides improvements in battery pastes which may be used with conventional paste mixing processes, procedures and equipment to produce positive and/or negative battery plates having greater uniformity, more consistent quality, more consistent reproducibility, all while eliminating the curing process, procedure and equipment so as to reduce the cost and speed up the production of batteries.